1. Field of the Invention
The present invention relates to a polymer powder, a curable resin composition including the polymer powder and a cured material thereof
2. Description of Related Art
Following the progresses in the information technology (IT) related equipments, including mobile equipments, digital household appliances, telecommunication equipments and automobile electronic equipments, the resin raw materials used in the field of electronics attract much attentions. The needs for the thermosetting resins such as epoxy resins, polyimide resins, acrylic series curable resins and oxetane series curable resins with excellent heat resistance and insulating property, or the active energy ray curable resins are drastically increased.
For a luminant device such as an optical semiconductor in practical applications such as display panels, light sources for image reading, and traffic display units, the majority was manufactured by sealing with resins. As the sealing resins, the epoxy resins were extensively used owing to their excellent mechanical properties, electrical insulation and adhesive properties. Among them, the alicyclic epoxy resins were mostly used as the sealing resins for the optical semiconductors due to their excellent transparency and heat resistance.
Especially, the epoxy resins that are in the liquid form at the ambient temperature may be used as materials for a variety of pastes or films, because they can be molded or coated at the ambient temperature. However, for the epoxy resin composition, due to high dependence of its viscosity on temperature, its viscosity significantly drops with temperature elevation until being cured. Hence, precise processing, such as precise filling or coating by dispensers, formation of precise pattern by screen printing, and coating on the film with high precision of film thickness, becomes difficult. Especially in the field of electronic materials, the requirements of precision for the processing are increased year by year, and for the epoxy resin compositions used, it is highly demanded that the viscosity does not drop even when the temperature is elevated, or the shape becomes stabilized as early as possible.
The method for imparting the aforesaid characteristics to the epoxy resin compositions includes: formulating specific vinyl polymers, as the gel-forming agent (hereinafter as “pre-gelling agent”), in the epoxy resin composition for turning the epoxy resin composition into a gel state rapidly by heating.
In Patent document 1, a method of using the specific vinyl polymer as the pre-gelling agent is proposed.
On the other hand, for the alicyclic epoxy resins, despite their high transparency and heat resistance, these resins has the following characteristics, i.e., the epoxy resin cured materials obtained from curing are poor in crack resistance (for example, they often have crack damages caused by cold-heat cycles), so that they are ineligible for applications requiring reliability over a long period. In terms of the generation of cracks, it is believed that it is primarily caused by difference of the linear expansion coefficients between the epoxy resin cured materials and the inorganic material as well as the elastic modulus of the epoxy resin cured material, and the generation of cracks may be prevented by increasing the glass transition temperature and reducing the linear expansion coefficients and the elastic modulus of the epoxy resin cured materials. In Patent documents 2˜4, a method of formulating acrylic series rubber particles is disclosed, as one method for reducing the elastic modulus of the epoxy resin cured materials.
Furthermore, in Patent document 5, disclosed is a method of formulating specific (meth)acrylate-based polymers in the epoxy resin composition to improve impact resistance, adhesive and gelling properties.